1. Field of the Invention
This invention relates to a method and an apparatus for error correction which are applied to digital information data when digital information signals are transmitted through a transmission line, such as an optical fiber, and to a method and an apparatus for reproducing the digital information signals coded thereby.
2. Description of the Prior Art
In an optical digital audio disc system (generally referred to as a compact disc system), a "mother" disc, a "stamper" disc, or the like is produced on the basis of the data reproduced from a master tape by an optically cutting apparatus similarly to a conventional analog disc. On such a "mother disc, a main channel consisting of digital audio signals and subcoding channels consisting of the data for control, display, or the like, and frames and syncs are recorded in spiral-like signal tracks. A number of replica discs are stamped from the "mother" disc.
Error correction coding processing which is described in detail in application Ser. Nos. 274,262, filed June 16, 1981, now abandoned; 275,328, filed June 19, 1981, now abandoned; 283,924, filed July 6, 1981, now abandoned; 536,824, filed Sept. 28, 1983, now U.S. Pat. No. 4,476,562, issued Oct. 9, 1984; 579,033, filed Feb. 15, 1984, now U.S. Pat. No. 4,497,058, issued Jan. 29, 1985; 613,761, filed May 24, 1984, now abandoned; and 684,161, filed Dec. 21, 1984 is performed with respect to the main channel. Eight channels called P, Q, R, S, T, U, V, and W are provided for the subcoding channels. The P and Q channels among these eight subcoding channels are used for selection of music programs and for rapid access operation to reproduce the beginnings of music programs when a compact disc is played back. Display data or audio data is interposed in the remaining six channels R through W. For example, picture of audio data to explain a composer, performers, or the like of a music program recorded in the main channel is recorded in these 6 channels R-W.
It is necessary to record in these subcoding channels not only the data to be actually displayed and output but also control data such as instructions or the like to indicate the kind of above-mentioned inherent output data and to process the data in the subcoding channels. However, the data format of the subcoding channels is not defined in detail and a method for error correction thereof has not previously been proposed. Furthermore, this control data is required in order to correctly process the display or audio data in the subcoding channels and is more significant than the display or audio data. Therefore, to the extent possible, it is necessary to prevent the control data from including errors upon playback.